Acid-base properties and the directions of oxidative transformation of methane over nickel-based catalysts

Two completely different behaviors of the oxidative transformation of methane (OTM) were performed on nickel-based catalysts because of different acid-base properties of those catalysts. The relatively acidic LaNiOx and LiNiLaOx/Al2O3 catalysts exhibit excellent performances in the partial oxidation of methane to syngas (POM). However, the relatively basic LiNiLaOx catalyst has a good performance in the oxidative coupling of methane to C-2 hydrocarbons (OCM). The redox behaviors of those catalysts and the states of the nickel present were investigated by TPR techniques. TPR results indicated that the active component nickel of the working LaNiOx and LiNiLaOx/Al2O3 catalysts existed in the reduced state, and that of the working LiNiLaOx catalyst existed in the oxidized state under the same reaction conditions. It can be concluded that the acidic property favors keeping the reduced nickel and the reduced nickel is necessary for the POM reaction, whereas the basic property favors keeping the oxidized nickel and the oxidized nickel is necessary for the OCM reaction.